The present invention relates to flow control valves and, more particularly, to a valve for controlling the flow of water from a pressurized water tank to a toilet bowl in an aircraft, train or other transportation vehicle.
In most vacuum flush aircraft toilet systems, flushing water is supplied to the toilet bowl by a water supply line connected between the bowl and a water tank containing the aircraft's potable water supply. After the supply line is pressurized and the toilet system is ready for use, a valve connected in the supply line between the tank and the bowl regulates the amount of flush water admitted into the bowl. In most vacuum flush systems, this valve must possess several characteristics to provide for proper operation and maintenance of the system. For example, once the water supply line has been pressurized, the valve must be closed when the toilet bowls are not in use to prevent water from constantly entering the bowl and overflowing into the cabin floor. Water overflow from the bowl is of serious concern because detrimental corrosive action on structural members of the aircraft by the water, among other things, may occur. The valve also must be capable of opening and closing to permit a predetermined volume of water to enter and flush waste from the bowl. Since water from the aircraft's potable water supply is somewhat limited, opening and closing of the valve must be relatively precise. Under present airline standards, only eight ounces of water, or less, is supplied for each bowl flushing operation.
Another concern involves situations where the aircraft will not be used and is stored in an environment subject to freezing temperatures. Even though the aircraft's potable water tank may be drained and the water supply line thus is not pressurized in these situations, water normally remains trapped in the upper end of the water supply line between the closed valve and the toilet bowl. As a result, freezing temperatures within the aircraft cabin during parking or storage of the aircraft can cause the water remaining in the line to freeze, and thereby expand and possibly burst the line. At best, the frozen water may be difficult to thaw and therefore may unduly delay or prevent operation of the system upon reactivating the aircraft. Since the water used to flush the toilet bowl comes from the potable water supply tank, anti-freeze additives cannot be put into the water to prevent freezing without contaminating the water and preventing its other necessary uses within the aircraft. Thus, the water valve should be capable of draining this remaining water in the lines when the lines are not pressurized.
Previous valve configurations generally have proven unsatisfactory in accommodating the variety of situations encountered during the operation and maintenance of the vacuum flush system, as described above. For example, one known valve construction includes a valve housing having an axial bore with a valve seat surrounding the bore at one end of the housing. The valve also includes a hollow plug movable within the bore between open and closed positions. In the open position, the supply line to which the valve is connected is unpressurized, and the plug is spaced from the seat to permit draining. In the closed position, the water line is pressurized, forcing the plug against the valve seat to stop flow. Selective opening and closing of the valve when the line is pressurized is accomplished by a solenoid. The valve described above, however, is prone to leakage unless the water pressure is sufficiently high. As such, the valve is not sufficiently reliable.
Accordingly, there has existed a definite need for a water valve which closes when the water supply line is pressurized, which will temporarily open and close to permit a predetermined volume of water to enter and flush waste from the bowl, which will conveniently drain the remaining water in the line when the system is not pressurized, and which is inexpensive to manufacture and requires little maintenance. The present invention satisfies all of these needs and provides further related advantages.